1. Field of the Invention
The invention relates to an apparatus and method for remediating soil and producing hot mix asphalt (HMA) and, more particularly, relates to a combined soil remediation and HMA plant 1) having a soil incinerator and a dryer, 2) exhibiting improved soil incineration characteristics, and 3) employing a combination afterburner/gas transfer duct leading from the soil incinerator to the dryer.
2. Discussion of the Related Art
Soil remediation systems, though relatively new, are well known. The traditional soil remediation system drives volatile contaminants from soil in a primary treatment unit (typically a rotating drum-type incinerator) and incinerates a portion of the volatile contaminants therein, then conveys the remaining volatile contaminants to a separate afterburner for combustion. Destruction of the contaminants requires that the temperatures within the primary treatment unit be maintained within an appropriate temperature range (typically between 1400.degree. F. and 2000.degree. F.) for a sufficient time and in the presence of adequate oxygen for complete contaminant incineration. The reclaimed soils discharged from the system, being organically inert and thus not reusable for most purposes, traditionally were buried in landfills or otherwise discarded.
Soil remediation systems of the type described above exhibited marked drawbacks and disadvantages. Large quantities of heat were required both for soil remediation in the incinerator and for contaminant incineration in the afterburner. The residual heat from these processes traditionally was dissipated without being put to use and thus was wasted. Moreover, the hot incinerated soil required rather cumbersome and expensive systems to quench and moisten the reclaimed soil and to inhibit the release of dust and vapors from the primary treatment unit as well as the reclaimed soil.
Various systems have been proposed to alleviate one or more of the problems associated with traditional soil remediation systems. For instance, U.S. Pat. No. 5,129,334 to Mize (the Mize patent) discloses a system which combines a soil remediation process with a hot mix asphalt (HMA) production process. In the system disclosed in the Mize patent, the discharge end of a rotary aggregate dryer and the discharge end of a rotary soil incinerator are enclosed by a common breaching or shroud which receives both the heated and dried aggregate from the dryer and the reclaimed soil from the incinerator. A diverter gate is positioned in the breaching to permit the soil to be selectively mixed with the aggregate.
The system disclosed in the Mize patent, though satisfactory, exhibits several drawbacks and disadvantages.
First, because the rotary incinerator must be dimensioned and configured so as to fit within the common shroud, the incinerator size relative to that of the dryer is limited. In practice, the incinerator cannot have a diameter which is significantly larger than one-half the diameter of the dryer.
Second, any volatilized hydrocarbons and other contaminated products which are not incinerated in the incinerator are drawn into the dryer where there is substantial risk that they will be exhausted from the dryer without being incinerated. The Mize patent recognizes this problem and attempts to address it by providing tuyeres or apertures along the length of the rotary incinerator which supply additional air for the staged combustion of fuels and combustible contaminants in the soil. These tuyeres, however, are only partially effective and increase the complexity of the system. Moreover, providing a relatively small diameter incinerator chamber necessarily increases the velocity of gases flowing therethrough and limits the retention time of volatilized gases and contaminated dust particles in the chamber, thereby reducing further the effectiveness of the unit.
Third, it is very difficult to obtain a soil sample from Mize's arrangement because the reclaimed soil is discharged directly from the incinerator into the common shroud and mixed with heated and dried aggregate before it is available for inspection.